This invention relates to an improved document feeding system for an electrostatic reproduction machine, but more particularly to apparatus including a conveyor or transport belt for moving a document across a scanning station and means for easily and very accurately positioning any one of a plurality of documents of various sizes directly on the belt so that the document is properly located with respect to the scanning station as the document is moved over the latter.
In a conventional electrostatic reproduction machine a xerographic plate (photoreceptor) comprising a layer of photosensitive insulating material affixed to a conductive backing is used to support electrostatic latent images, the plate being in the form of a drum or an endless belt, for example. In the xerographic process, the photosensitive surface is electrostatically charged, and the charged surface is then exposed to a light pattern of the image being reproduced to thereby discharge the surface in the areas wherein light strikes the surface. The undischarged areas of the surface thus form an electrostatic charge pattern (an electrostatic latent image) conforming to the original pattern. The latent image is then developed by contacting it with a finely divided electrostatically attractable powder referred to as "toner". Toner is held on the image areas by the electrostatic charge on the surface. Where the charge is greater, a greater amount of toner is deposited. Thus, a toner image is produced in conformity with a light image of the copy being reproduced. Generally, the developed image is then transferred to a suitable transfer member (e.g., paper), and the image is affixed thereto (e.g., by heat fusing) to form a permanent record of the original document.
In the practice of xerography, the transfer member is caused to move in synchronized contact with the photosensitive surface during the transfer operation, and an electrical potential opposite from the polarity of the toner is applied to the side of the paper remote from the photosensitive surface to electrostatically attract the toner image from the surface to the paper.
In modern electrostatic reproduction machines, it is often necessary to move documents across a scanning station in order to produce the latent image on the photosensitive surface. In one prior art arrangement of a document feeding system, only documents of a certain width can be handled without the use of a special carrier to place the document in as it moves through the machine. In addition, this arrangement uses grippers to grip the lead edge of the document as it moves through the machine, and the grippers "print-out" onto the copy made. Also, the grippers tend to tear or deface the document if the latter is very thin. In other prior art arrangements, if the operator does not release the document at the proper time, the document may be improperly positioned as it moves through the machine and across the scanning station. In some instances it is difficult for the operator to properly register the document because the document registration mechanism is out of the sight of the operator. Thus, what is needed is a document feeding system which overcomes the problems of these prior art arrangements.